Grounded sleeve antenna



GROUNDED SLEEVE ANTENNA 2 Sheets-Sheet 1 Filed March 24, 1965 INVENTORS JOHN 11 KUL/K 'RICHARO E SCHMIDT h vAGENT ATTORNEY Jan. 30, 1968 J. J. KULIK ETAL 3,366,962

GROUNDED SLEEVE ANTENNA Filed March 24, 1965 2 Sheets-Sheet 2 v 1AA INVENTORS UOH/V J. KUL/K RICHARD H SCHMIDT BY 6 AGENT ATTORNEY United States Patent 3,366,962 GROUNDED SLEEVE ANTENNA John .I. Kulik, Ventnor, N.J., and Richard F. Schmidt, Washington, D.C., assignors to the United States of America as represented by the Secretary of the Navy Filed Mar. 24, 1965, Ser. No. 442,560 12 Claims. ((51. 343-790) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to grounded sleeve antennas, and more particularly to such antennas in which minimum height, maximum bandwidth, above ground feed, and inherent impedance matching qualities are desired.

The grounded sleeve antenna has enjoyed success as a multipurpose communication antenna. Its widespread use, however, has served to point up certain structural features which can be improved for even greater versatility. With antenna sites located near airfields in many instances, it is desirable to top the antennas with warning lights. Also, the height of the antennas may be shortened to alleviate the hazard to low flying aircraft. If, in addition, the bandwidth of the antenna is increased, the resulting device has advantageous features for most applications. It has also been found desirable to have the radiating elements of the antenna constructed of wires simultating the surfaces thereof. This feature alone saves considerably in the cost of each unit, allays possible enemy detection, is less susceptible to damage by wind and is a considerably less expensive means of construction.

The antenna may be equipped with warning lights and also protected from lightning by utilizing a conductive grounded mast which can be hollow to serve as a conduit for the lighting wires. When the sleeve element is also grounded, the antenna is protected from short-circuiting by floods and a step toward impedance matching inherent in the antenna design has been taken. This desired feature of built-in impedance matching may be further augmented by sleeve modification to achieve a considerably improved grounded sleeve antenna.

The antenna of the present invention is a grounded sleeve antenna incorporating the above described features into its basic design while continuing to provide broad band transmission without sacrificing the excellence of transmission characteristics normally attributed to grounded sleeve antennas.

It is, accordingly, an object of the present invention to provide an electrically short broadband antenna suitable for both ship and shore installation.

Another object is to provide an antenna protected against damage from lightning, wind or flood.

Another object is to provide a grounded sleeve antenna having its radiating surfaces simulated by wire construction.

A further object of the present invention is to provide an antenna adapted to support aircraft warning lights without distortion of the transmission characteristic due to the lighting wires and without use of special lighting transformers.

It is another object to provide an antenna capable of matching the impedance of associated transmitting and receiving equipment as an inherent feature of the antenna design.

Other objects and advantages of the invention will become more fully apparent from the following description of an exemplary embodiment of the invention, as illustrated in the accompanying drawings, in which:

FIG. 1 is a diagramatic view of an antenna representing the present invention;

FIG. 2 shows an alternative method of antenna feed;

FIG. 3 is a top detail of the upper radiating element; and

FIG. 4 shows a perspective view of the sleeve portion of an antenna typical of the present invention.

Referring now to the drawings in which like characters refer to like elements throughout, there is shown in FIGS. 1 and 4 an embodiment of the antenna chosen for purposes of illustration situated on a ground plane 11. The antenna has an electrically conductive mast 14 and a lower radiating element or sleeve 12 making electrical contact with said ground plane. The conductive mast 14 passes through an orifice 23 in the top surface 22 of said sleeve radiating element and supports an upper radiating element 13 in the shape of a frustrum. Both the upper radiating element, affixed to and in electrical connection with mast 14, and the sleeve radiating element, electrically isolated from mast 14 except at the ground plane, may be entirely constructed of wires with appropriate support members not shown. The wires of sleeve 12 are indicated as 16 in FIGS. 1 and 4, while those wires forming the upper radiating element are indicated as 17 in FIGS. 1 and 3.

FIGS. 1, 2 and 4 show various arrangements of the feed to the antenna. Coaxial feeder transmission line 15 is shown in FIG. 1 contiguous with the mast 14 to a point somewhat below the top of the sleeve radiating element 12. The outerconductor 21 of feeder 15, as shown in this figure, is connected to and in efiect merges with the inner conductor-mast of the antenna, while the outer conductor-sleeve element of the antenna is connected to the inner conduct or 20 of the feeder at the feed point 25.

FIG. 2 shows the coaxial transmission line 15 brought up to the feed point 25 within the mast, which is hollow at least to the point of feed for this purpose. Here too, the center conductor 20 of the transmission line 15 connects to the sleeve at the feed point while the outer conductor 21 of the feed line connects to the conductive mast. The mast has ports 24 at feed point 25 to permit this connection.

FIG. 4, shows a somewhat different feed connection, while the feed point 25 is at the same elevation, i.e. slight- 1y below the top of the sleeve radiating element of the antenna. Here the transmission line is contiguous with the inner wall of the sleeve from the ground plane to the feed point. Unlike the feed connection scheme shown in FIGS. 1 and 2, the outer conductor of the transmission line connects to the sleeve, or outer conductor of the antenna, while the inner conductor of the transmission line is connected to the inner conductor or mast of the antenna, and thus there is no coaxial inversion as in the above described embodiments, which coaxial inversion will be described below.

FIGS. 1, 2 and 4 show that the lead connection is not directly to the sleeve radiating element proper but to an element designated 19 contained within this sleeve. Since the impedance of a coaxial transmission line is related to the ratio between the diameters of the inner and outer conductors thereof, the change in the size of the feeder transmission line from that generally designated 15 to the coaxial conductor represented by the antenna itself can represent a sizable change of impedance relative to the feeder impedance. To minimize this mismatch, the outer conductor (sleeve) of the coaxial antenna has been effectively reduced in size to that shown by the shield element designated 19, such that the impedance match between the transmission line and the antenna is improved, Element 19 in conjunction with the mast constitutes a series-connected high impedance coaxial insertion transformer, constituting an expanded extension of the coaxial transmission 3 line 15. This element encircles the mast 14 and extends from the top of the sleeve 12 to the feed point 25. The length of this element is also determined by an optimum impedance match. The series impedance transformer 19 effectively transposes the feed point 25 to the top of the sleeve element, there forming a 'vertual feed point 26.

In FIGS. 1 and 2 the series-connected impedance transformer formed by shield 19 and the mast constitutes an inverted extension of the feeder transmission line 15. The inversion results from the center conductor 20 of the feeder transmission line connected to the outer conductor 19 of the series impedance transformer, while the outer conductor 21 is extended as the inner conductor-mast of the series impedance transformer.

The connection of the sleeve radiating element to the ground plane at the base of this radiating element places this element in electrical common with the mast at the ground plane. The ground plane 11 thus constitutes a short circuit to this coaxial section. The height of the sleeve from the ground plane to the plane of the connecting means 18 constitutes a short-circuited stub of this length primarily at the lower frequencies of transmission. The impedance of this section of the antenna, dependent upon the ratio of the diameter of the sleeve to the diameter of the mast is connected in parallel with the series impedance transformer 19 by the conducting plane or disc 18 shown in FIGS. 1 and 4, which also may be of wire construction. It is thus the combination of these two impedance-matching devices that enables this broadband antenna to closely match the impedance of the transmitting or receiving equipment over the entire frequency band.

FIG. 3 is an illustration of one possible configurationof the upper radiating element of the antenna, as indicated by the top surface thereof. Shown here is a simulated top surface of wire construction substantially square shaped. It should be understood that the particular shape of the radiating elements of the antenna is not critical except for bandwidth and distortion considerations. Thus, the upper radiating element may take the shape of a truncated cone instead of the truncated pyramid shown. The sleeve radiating element also may be cylindrical or cubic in shape or assume any other configuration symmetrical about the mast which has its side surfaces substantially parallel to that central member. It should also be noted that while wire construction is preferred for low wind resistance and low susceptability to enemy detection, the radiating surfaces and the shield element 1? may be of solid material.

One of the objects of the present invention is to provide an electrically short broadband antenna. The illustrated embodiment has been tested and found to have a height of 0.145 wavelength at the low end cutoff of the frequency band (predicated on pattern and 3:1 VSWR considerations), while radiating electromagnetic energy over a 12 to 1 frequency band. These desirable features have been obtained by the use of unusually wide radiating elements. The inverted frustrum upper radiating element with its wide base at the top of the antenna provides the horizontal capacitance top-loading of the antenna for inincreased low frequency performance.

In addition to the function of impedance matching, the shorted sleeve to mast at the ground plane and the above ground feed point insures continued operation during flood conditions. The grounded mast also serves as a lightning arrester While providing a conduit path for aircraft warning light wires without the customary use of special lighting transformers. The electrically conductive grounded mast also is a feature making the antenna desirable for ship board use.

The extremely broadband transmission characteristics of the antenna of the present invention enables this device to be used as a multichannel antenna, thereby replacing the individual antennas ordinarily used for each communication channel.

Since various changes and modifications may be made in the practice of the invention herein described without department from the spirit or scope thereof, it is intended that the foregoing description shall be taken primarily by way of illustration and not in limitation except as may be required by the appended claims.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. An electrically short broadband antenna, comprising:

a ground plane;

an electrically conductive mast grounded to said ground plane at the base of said mast;

a sleeve radiating element encircling the lower portion of said .mast and being connected to said ground plane at the base of said sleeve radiating element;

an upper radiating element being electrically in common with said mast and affixed thereto, such that substantially all of said mast above said sleeve radiating element is encompassed by said upper radiating element;

a coaxial feeder transmission line;

a shield element encircling said mast and forming with said mast a series-coupled extension of said coaxial feeder transmission line, whereby the feed point of said antenna at the connection of said shield element and said mast with said feeder transmission line is effectively brought to the top of said sleeve radiating element; and

conductive means connecting said sleeve radiating element to said shield element, whereby the impedance changeoccasioned by the short-circuit between the sleeve radiating element and the mast at said ground plane is coupled in parallel at the feed point of said antenna with the series impedance transforming element formed by said shield element and said mast.

2. An antenna as recited in claim 1, wherein said sleeve radiating element has a top surface substantially parallelto said ground plane, which surface contains an orifice permitting said mast to pass therethrough.

3. An antenna as recited in claim 1, wherein the radiating side wall of said sleeve radiating element is substantially parallel to said mast.

4. An antenna as recited in claim 1, wherein said sleeve radiating element and said upper radiating element consist of wires simulating solid surfaces for these elements.

5. An antenna as recited in claim 1, wherein said shield element and said sleeve radiating element form concentric cylinders about said mast.

6. An antenna as recited in claim 1, wherein said upper radiating element is in the shape of a frustrum, the larger end of which is substantially at the top of said mast.

7. An antenna as recited in claim 6, wherein said upper' radiating element is bounded by an upper and a lower surface substantially parallel to said ground plane.

8. An antenna as recited in claim 1, wherein said shield element extends longitudinally of said mast from the top of said sleeve radiating element'to said feed point slightly below the top of said sleeve radiating element, the length and characteristic impedance of said series impedance transforming element formed by said shield element and said mast being determined for an optimum impedance match.

9. An antenna as recited in claim 8, wherein the outer conductor of said coaxial feeder transmission line is in electrical common with said mast and the center conductor of said coaxial feeder transmission line is coupled to said sleeve radiating element by said shield element.

10. An antenna as recited in claim 9, wherein said mast is hollow and said coaxial feeder transmission line is contained within said mast;

. said mast being ported at said feed point to permit connection of the center conductor of said coaxial feeder transmission line to said shield element.

11. An antenna as recited in claim 8, wherein the outer conductor of said coaxial feeder transmission line is l t lfiqtigfil common with said sleeve radiating element and the center conductor of said coaxial transmission line is connected to said mast substantially at the base of said series impedance transforming element.

12. An electrically short broadband antenna, comprisa ground plane;

an electrically conductive mast grounded to said ground plane at the base of said mast;

a sleeve radiating element encompassing the lower portion of said mast and being connected to said ground plane at the base of said sleeve radiating element;

said sleeve radiating element having a top surface substantially parallel to said ground plane, which surface contains an orifice permitting said mast to pass therethrough;

said sleeve radiating element being electrically independent of said mast except at said ground plane;

an upper radiating element in the shape of a frustrum, the larger end of which is substantially at the top of said mast;

said upper radiating element being electrically in common with said electrically conductive mast and affixed thereto, such that substantially all of said mast above said sleeve radiating element is encompassed by said upper radiating element;

said sleeve radiating element and said upper radiating element being composed of Wires which simulate solid surfaces for these elements;

said upper radiating element being bounded by an upper and a lower surface substantially parallel to said ground plane;

a coaxial feeder transmission line, the outer conductor of which is in electrical common with said mast;

a shield element extending along and encircling said mast from a point slightly below the top of said sleeve radiating element to the top of said sleeve radiating element;

said shield element and said mast forming a series impedance transforming element, the length of said series impedance transforming element being determined for an optimum impedance match over the transmission band of said antenna;

said shield element being disposed between said sleeve radiating element and said mast;

said shield element being connected to the center conductor of said coaxial feeder transmission line at the feed point of said antenna formed by the connection of said series impedance transforming element with said feeder transmission line, such that a virtual feed point is effectively created at the top of said sleeve radiating element and said shield element with said mast forms an enlarged inverted extension of said feeder coaxial transmission line;

and conductive means connecting said sleeve radiating element to said series impedance transforming element, whereby the impedance change occasioned by the short circuit between the sleeve radiating element and the mast at said ground plane is coupled in parallel with said series impedance transforming element at the feed point of said antenna.

No references cited.

ELI LIEBERMAN, Primary Examiner. 

1. AN ELECTRICALLY SHORT BROADBAND ANTENNA, COMPRISING: A GROUND PLANE; AN ELECTRICALLY CONDUCTIVE MAST GROUNDED TO SAID GROUND PLANE AT THE BASE OF SAID MAST; A SLEEVE RADIATING ELEMENT ENCIRCLING THE LOWER PORTION OF SAID MAST AND BEING CONNECTED TO SAID GROUND PLANE AT THE BASE OF SAID SLEEVE RADIATING ELEMENT; AN UPPER RADIATING ELEMENT BEING ELECTRICALLY IN COMMON WITH SAID MAST AND AFFIXED THERETO, SUCH THAT SUBSTANTIALLY ALL OF SAID MAST ABOVE SAID SLEEVE RADIATING ELEMENT IS ENCOMPASSED BY SAID UPPER RADIATING ELEMENT; A COAXIAL FEEDER TRANSMISSION LINE; A SHIELD ELEMENT ENCIRCLING SAID MAST AND FORMING WITH SAID MAST A SERIES-COUPLED EXTENSION OF SAID COAXIAL 